1. Technical Field
The present invention relates to a vehicle steering gear and, particularly, to a fluid power assist rack and pinion steering gear with end-take-off.
2. Description of the Prior Art
Fluid power assist rack and pinion steering gears with end-take-off for vehicles are known. U.S. Pat. No. 4,211,152 discloses such a steering gear. The steering gear of U.S. Pat. No. 4,211,152 includes a rack housing for attachment to a vehicle. A rack member is supported in the housing for axial movement relative to the rack housing. Axially opposite ends of the rack member are connected to a respective ball and socket joint of respective tie rods which are associated with the steerable wheels of the vehicle. Rack teeth are formed on the rack member adjacent one of its axial ends. A rotatable pinion gear is in meshing engagement with the rack teeth. A fluid motor is associated with the rack member to provide a power assist toward movement. The fluid motor includes a piston fixed to the rack member, located in a fluid chamber of the fluid motor, and movable with the rack member. The piston is located between end walls of the fluid chamber and divides the fluid chamber into a pair of power assist fluid working chambers.
The rack member is movable from an initial position in opposite directions. A rack tooth at one end of the rack is spaced apart from a rack tooth at the other end of the rack a distance which defines a length of travel of the rack member. Seals are located in the opposite end walls of the fluid motor. The end walls of the fluid motor are spaced apart at least a distance equal to the length of travel of the rack member. The seals tightly encircle the periphery of the rack member to prevent fluid leakage from the working chambers.
The rack member has a relatively smooth surface adjacent the rack teeth for a length approximately one-half the length of travel of the rack member. The smooth surface spaces the rack teeth from one of the seals so the rack teeth cannot move to a position within the seal which could create fluid leakage. In its initial position, the piston is located a distance at least one-half the length of travel of the rack member from either end wall of the fluid chamber. The distance that the rack member extends axially outward of the rack housing must be at least equal to one-half the length of travel of the rack member so the ball and socket joints of the tie rods do not engage end walls of the housing.
The overall length of the rack member is defined as the sum of the lengths of portions of the rack member which are required to accommodate travel of the rack member plus the sum of the lengths of the piston, chamber end walls, bearing and spacing of the ball and socket joints along the rack member. The sum of the lengths of the portions of the rack member required to accommodate travel of the rack member must be at least three times the length of travel of the rack member. The exact length of travel of the rack member, and thus the overall length of the rack member, is dependent upon the requirements of the particular vehicle in which the steering gear is used.
Such a steering gear has a relatively long rack member. Thus, the steering gear occupies valuable space in the vehicle. It should be apparent that it is desirable to decrease the length of the rack to thereby decrease the amount of space required to package a steering gear in a vehicle, to reduce weight in the vehicle, and to provide for optimized vehicle steering characteristics which may require shorter rack lengths than are available from prior art end-take-off steering gears.